This invention relates to a phosphor wherein a solid solution formed of gallium nitride and indium nitride is doped with a doping material or dopant, and more particularly to a phosphor increased in both luminance characteristics and life characteristics which emits light by electron excitation and exhibits various kinds of luminous colors depending on selection of a starting material.
A phosphor including a matrix made of GaN obtained by subjecting Ga2O3 to nitriding in an ammonia atmosphere and Cd acting as a dopant is known in the art, as disclosed in Japanese Patent Application Laid-Open Publication No. 41686/1976. However, the phosphor disclosed is not applied to luminescence by electron excitation. This is revealed by the fact that the Japanese publication fails to teach and suggest luminescence of the phosphor by electron excitation.
Nitriding of Ga2O3 in a nitrogen atmosphere is started from a surface of Ga2O3. However, an increase in temperature causes Ga2O3 thus nitrided to be re-oxidized. More particularly, gallium nitride generally tends to release nitrogen therefrom, to thereby be an n-type and highly decreased in resistance, resulting in exhibiting luminescence even when it is not subjected to doping.
Luminescence of gallium nitride is carried out by pair luminescence of a donor (D) and an acceptor (A). Zn, Mg or the like may be used as the acceptor. The donor is a nitrogen defect naturally formed, so that an increase in concentration of the donor by the prior art causes an increase in nitrogen defect in the material, leading to a deterioration in crystallizability or crystallinity of the gallium nitride. Thus, the prior art fails to provide gallium nitride which has the number of donors controlled to a desired level.
The presence of oxygen possibly causes oxidation of gallium nitride. Thus, when Ga2O3 which is an oxide of gallium is used as the starting material, it is impossible to fully nitride Ga2O3. Also, even when gallium nitride is obtained, oxygen adversely affects luminescence of gallium nitride, to thereby fail to provide the phosphor with satisfactory quality.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present intention to provide a phosphor which is capable of being prevented from being adversely affected by oxygen.
It is another object of the present invention to provide a phosphor which is capable of permitting a concentration of a donor to be controlled, to thereby be increased in luminous efficiency.
It is a further object of the present invention to provide a phosphor which is capable of exhibiting various kinds of luminous colors by electron excitation depending on selection of elements added thereto.
It is still another object of the present invention to provide a phosphor which is capable of exhibiting both enhanced luminance characteristics and life characteristics.
In accordance with the present invention, a phosphor in the form of a columnar powder is provided. The phosphor is produced by heating a starting material constituted by a GaN based phosphor material to a temperature equal to or greater than a sublimation temperature thereof and represented by Ga1xe2x88x92xInxN:A,B, wherein x is larger than or equal to 0 and smaller than 1 (0xe2x89xa6x less than 1), A is selected from the group consisting of Zn and Mg, and B is selected from the group consisting of Si and Ge.
In a preferred embodiment of the present invention, the temperature described above is 1180xc2x0 C. or more.
In a preferred embodiment of the present invention, a ratio of a thickness of the phosphor to a length thereof is 1:1.5 or more.
In a preferred embodiment of the present invention, the phosphor has a half band width at 2xcex8=34xc2x0 in a X-ray diffraction pattern set to be below 0.2.